I have two Cairn Terriers. My active one suffers from flea allergies. She bites and chews herself and I can really tell she suffers from fleas. The older flea prevention medications were no longer effective. My Vet recommended Vectra. I read a number of negative reviews on the product and voiced my concern to my Vet. He assured me that Vectra was effective and none of his clientele's dogs had any issues. Since using Vectra my dogs have had no flea issues except Cory likes water and she goes swimming in the local creek. Toward the end of the thirty day period I start combing Cory for fleas and if I find any on her, bath and Vectra time, usually it last 30 days. Zee's application is good for more than 30 day but in order to stay consistent, I do both dogs at the same time. I highly recommend Vectra.